MB-11721: Add a snapshot marker respnose api to upr_message_producers

We will be sending acks for some snapshot markers and need an api to
put the bytes on the wire.

Change-Id: Ib0a2d8443fd1fb800319fca9160f38df8661deae
Reviewed-on: http://review.couchbase.org/39378
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>
Fix breakage in build to to invalid rebase

Change-Id: I9381d2c6da70242a0d18d01bfbca401fb2f52bf4
Reviewed-on: http://review.couchbase.org/39641
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-11708: set memcached_version to the sha1

Change-Id: I11f81c7285152c8ed350cbbdac5c178c09c1beaf
Reviewed-on: http://review.couchbase.org/39656
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>
Merge remote-tracking branch 'membase/3.0' into 301

Change-Id: I4d488282947608e4864cd3cbed1cf090271c993e